1. Field of the Invention
This invention relates to substituted activated methylene reagents and methods of using such reagents to form electron deficient olefins.
2. Brief Description of Related Technology
Fast curing adhesives are well known. Most of those types of adhesives are based on cyanoacrylate chemistry.
Cyanoacrylate adhesives are known for their fast adhesion and ability to bond a wide variety of substrates. They are marketed as “super glue” type adhesives. They are useful as an all-purpose adhesive since they are a single component adhesive, very economical as only a small amount will do, and generally do not require any equipment to effectuate curing.
Traditionally, cyanoacrylate monomers have been produced by way of a Knoevenagel condensation reaction between a formaldehyde precursor, such as paraformaldehyde, and an alkyl cyanoacetate (an activated methylene reagent) with a basic catalyst. During the reaction, cyanoacrylate monomer forms and polymerises in situ to a prepolymer. The prepolymer is subsequently thermally cracked or depolymerised, yielding cyanoacrylate monomer. This approach has remained essentially the same over time, though various improvements and variants have been introduced. See e.g. U.S. Pat. Nos. 6,245,933, 5,624,699, 4,364,876, 2,721,858, 2,763,677 and 2,756,251.
In U.S. Pat. No. 3,142,698, the synthesis of difunctional cyanoacrylates using a Knoevenagel condensation reaction is described. However, the ability to thermally depolymerise the resulting, now crosslinked, prepolymer in a reliable and reproducible manner to produce pure difunctional monomers in high yields is questionable [see J. Buck, J. Polym. Sci., Polym. Chem. Ed., 16, 2475-2507 (1978), and U.S. Pat. Nos. 3,975,422, 3,903,055, 4,003,942, 4,012,402, and 4,013,703].
A variety of other processes for producing cyanoacrylate monomers are known, some of which are described below. For instance, U.S. Pat. No. 5,703,267 defines a process for producing a 2-cyanoacrylic acid which comprises subjecting a 2-cyanoacrylate and an organic acid to a transesterification reaction.
U.S. Pat. No. 5,455,369 defines an improvement in a process for preparing methyl cyanoacrylate, in which methyl cyanoacetate is reacted with formaldehyde to form a polymer that is then depolymerized to the monomeric product, and in which the purity of yield is reported to be 96% or better. The improvement of the '369 patent is reported to be conducting the process in a polyethylene glycol) diacetate, dipropionate, or dibutyrate, having a number average molecular weight of 200-400, as the solvent.
U.S. Pat. No. 6,096,848 defines a process for the production of a biscyanoacrylate, which comprises the steps of esterifying a 2-cyanoacrylic acid or transesterifying an alkyl ester thereof to obtain a reaction mixture; and fractionally crystallizing the reaction mixture to obtain the biscyanoacrylate.
U.S. Pat. No. 4,587,059 defines a process for the preparation of monomeric 2-cyanoacrylates comprising the steps of (a) reacting (i) a 2,4-dicyanoglutarate with (ii) formaldehyde, cyclic or linear polymers of formaldehyde, or a mixture thereof, in the presence of between about 0.5 and about 5 mols of water per mol of 2,4-dicyanoglutarate, at an acid pH of about 3 to slightly less than 7, and at a temperature of about 70 to about 140, to form an oligomeric intermediate product, and (b) removing water that is present from step (a) and thermolyzing the oligomeric intermediate product for a period of time sufficient to effect its conversion to monomeric 2-cyanoacrylates.
Commercial production of cyanoacrylate monomers ordinarily relies on the depolymerisation of a prepolymer formed under Knoevenagel condensation reaction conditions, as noted above. Still today the Knoevenagel condensation reaction is believed to remain the most efficient and prevalent commercial method for producing high yields of monofunctional cyanoacrylates. Nevertheless, it would be desirable to not have to resort to thermally induced depolymerisation of a prepolymer produced by the Knoevenagel condensation reaction. This prospect may also enable facile access to highly useful difunctional monomers, such as so-called bis-cyanaocrylates or hybrid materials of cyanoacrylate and other polymerisable or reactive functionality.
Vijayalakshmi et al., J. Ad. Sci. Technol., 4, 9, 733 (1990) describes the synthesis of cyanoacetates and corresponding cyanoacrylates, including preparation from chloroacetic acid and its esters by subsequent reaction with sodium cyanide.
Guseva et al., Russian Chem. Bull., 42, 3, 478 (1993) describes functionalized cyanoacetates, some of which were used in the subsequent synthesis of corresponding cyanoacrylates [Guseva et al., Russian Chem. Bull., 43, 4, 595 (1994); see also Golobolov and Gruber, Russian Chem. Rev., 66, 11, 953 (1997)].
One of the functionalized cyanoacetates noted in the preceding paragraph is glycidyl cyanoacetate. While the synthesis and characterisation of glycidyl cyanoacetate has been reported (such as is described in the preceding paragraph), the synthesis, characterisation and provision of performance characteristics of the corresponding glycidyl cyanoacrylate have not to date been published.
Other cyanoacetates are known, such as those with siliconised functionalities. See e.g. Senchenya et al., Russian Chem. Bull., 42, 5, 909 (1993) and European Patent Document No. EP 0 459 617.
The preparation of mono-, di-, tri- and tetra-functional cyanoacetates as curatives for epoxy resins for adhesive applications has been described. See e.g. Renner et al., “Cure of Epoxy Resins with Esters of Cyanoacrylic Acid”, J. Polym. Sci., Polym. Chem. Ed., 23, 2341 (1985) and U.S. Pat. Nos. 4,202,920 and 4,512,357.
K-D. Ahn and H. K. Hall, “Synthesis and Polymerization of the Four 1,3-Di(cyano and/or Carbomethoxy)-Substituted Butadienes”, J. Polym. Sci.: Polym. Chem. Ed., 19, 629-44 (1981) is directed to the synthesis of 1,3-dielectronegatively substituted butadienes to ascertain their feasibility for use as monomers in radical and/or anionic polymerizations. Ahn and Hall concluded that “[t]hese 1,3-disubstituted dienes are too reactive toward polymerization to handle readily.” And that “[t]he new dienes are highly polymerizable and the syntheses are difficult to carry out in substantial quantities. These dienes are more reactive toward polymerization than any other mono- or di-electronegatively substituted 1,3-butadienes reported to date.” Examples of these butadienes include
Only the second and third compounds listed above were reported by Ahn and Hall to have been isolated.
Absent from the published literature, however, are methods of using substituted activated methylene reagents to form electron deficient 1,3- or 1,3,3-substituted butadienes, which would be useful in the formation of curable compositions prepared therefrom. Until now.